The present invention relates to the general field of turbomachine blades made of composite material comprising fiber reinforcement densified by a matrix.
The intended field is that of rotor wheels having composite material blades for use in aeroengines or in industrial turbines.
Proposals have already been made to fabricate turbomachine blades out of composite material. For example, reference may be made to the French patent application FR 08/58090 (not yet published) filed jointly in the names of Snecma and Snecma Propulsion Solide that describes fabricating a turbomachine blade by making a fiber preform by three-dimensional weaving and by densifying the preform with a matrix.
When a rotor wheel has blades that are made of metal, the wheel generally has a plurality of metal blades mounted via their roots on a metal disk, and a metal casing is placed around the rotor wheel.
During assembly (when cold) of the rotor wheel inside the casing, it is necessary to leave radial clearance between the tips of the blades and the casing that surrounds the rotor wheel. However, in operation (when hot), this clearance may give rise to leakage of gas between the tips of the blades and the casing.
In order to reduce the risk of such leakage appearing, the free ends of the blades are generally provided with radial labyrinth teeth, and an abradable material is mounted on the inside surface of the casing in register with the labyrinth teeth. In operation of the rotor wheel, the disk, the blades, and the casing surrounding the wheel expand so that the labyrinth teeth carried by the blades abrade the abradable material carried by the casing. As a result, the clearance that is left on mounting between the tips of the blades and the casing tends to disappear, thereby limiting gas leakage.
In contrast, when a rotor wheel has blades that are made of composite material, the differences of expansion between the wheel (made in part out of the composite material of its blades) and the casing (made of metal) can be considerable. As a result, when operating while hot, the radial clearance that is left on mounting between the labyrinth teeth of the blades and the abradable material of the casing does not disappear completely, thereby having the consequence of sealing between the rotor wheel and the casing no longer being properly provided.